Plasma treatment apparatus and control method thereof

ABSTRACT

A frequency control circuit ( 45 ) controls an oscillation frequency of a second high frequency power source  51  based on a phase difference between a voltage component and a current component measured by a phase difference sensor ( 41 ) and an input impedance to an impedance matching device ( 34 ) measured by an impedance sensor ( 42 ). An amplitude control circuit ( 44 ) controls a level of a high frequency electricity output by the second high frequency power source ( 51 ) based on an electricity (effective electricity) which is measured by a power sensor ( 40 ) and is to be supplied to the impedance matching device ( 34 ).

TECHNICAL FIELD

The present invention relates to a plasma processing apparatus whichapplies a process such as a film forming process and the like to aprocess target by using plasma.

BACKGROUND ART

In the process of manufacturing a semiconductor device, a plasmaprocessing apparatus for applying a process to the surface of asemiconductor substrate by using plasma is used. As a plasma processingapparatus, for example, an apparatus for applying a Chemical VaporDeposition (CVD) process is known. Among plasma processing apparatuses,a parallel plate type plasma processing apparatus is widely used becauseit is excellent in process evenness and the apparatus structure isrelatively simple.

Such a plasma processing apparatus as described above employs animpedance matching device including variable reactance elements, inorder to reduce the electricity of a reflected wave from a plasma loadto a high frequency power source. The impedance matching device has, forexample, a capacitor, and can change its capacitance by a mechanicalmovement such as rotating an electrode constituting the variablecapacitor by, for example, rotation-driving a motor based on results ofmeasuring the electricity of a progressive wave, the electricity of areflected wave, etc. In other words, the impedance matching device canobtain a match between the output impedance of a high frequency powersource and the input impedance to an electrode of the plasma processingapparatus, by changing element constants (capacitance, inductance, etc.)of the built-in variable reactance elements such as the variablecapacitor and a variable inductance, etc.

In a case where a process condition is changed, the impedance of theplasma load is greatly changed. Therefore, it is necessary to largelychange also the impedance of the impedance matching device.

In this case, if the impedance matching device tries to obtain a matchof the impedances by allowing the variable reactance elementsconstituting the impedance matching device to be adjusted within a largevariable range, the range of fluctuation of the variable elements willbe inevitably too large. Therefore, there is a problem that it takes along time to reach the matched state, and the time required forprocessing a substrate is elongated.

Further, according to the above-described prior art, the elementconstants of the variable reactance elements are changed by a mechanicalmovement such as rotation-driving of a motor. Therefore, there is aproblem that a long time, for example, equal to or more than severalseconds, is required for obtaining a match of the impedances.Furthermore, even if the impedance matching device tries to minutelyadjust the capacitance of the variable capacitor in response to a changein the characteristic of the plasma, it is difficult to accuratelyadjust the impedances because of the roughness of the mechanicalcontrol. As a result, the plasma becomes unstable in some case.

DISCLOSURE OF INVENTION

The present invention was made in consideration of the above-describedcircumstance, and it is an object of the present invention to provide aplasma processing apparatus which can shorten the time required forsubstrate processing, and a method of controlling such a plasmaprocessing apparatus.

It is another object of the present invention to provide a plasmaprocessing apparatus which can generate stable plasma, and a method ofcontrolling such a plasma processing apparatus.

It is yet another object of the present invention to enable high-speedor accurate adjustment of impedances.

To achieve the above objects, a plasma processing apparatus according toa first aspect of the present invention comprises:

-   -   a vacuum container (2) in which a substrate is processed with        use of a plasma gas;    -   a plasma generation electrode (5) which is provided in the        vacuum container;    -   a high frequency power source (51) which generates a high        frequency electricity to be supplied to the plasma generation        electrode (5);    -   an impedance matching device (34) which matches an input        impedance of said plasma generation electrode (5) and an output        impedance of said high frequency power source (51);    -   an impedance sensor (42) which measures a level of an input        impedance of said impedance matching device; and    -   a frequency control circuit (45) which controls an oscillation        frequency of the high frequency power source based on a        measurement result from the impedance sensor.

There may further be provided a phase difference sensor (41) whichmeasures a phase difference between a voltage component and a currentcomponent of an electricity to be supplied to the impedance matchingdevice, and the frequency control circuit (45) may control theoscillation frequency of the high frequency power source based onmeasurement results from the phase difference sensor and the impedancesensor.

There may further be provided a power sensor (40) which measures anelectricity to be supplied to the impedance matching device from thehigh frequency power source, and an output control circuit (44) whichcontrols an output electricity of the high frequency power source basedon a measurement result from the power sensor.

There may further be provided a selector (43) which switches selectionbetween the phase difference sensor (41) and the impedance sensor (42)to obtain measurement results from both of them, and the frequencycontrol circuit (45) may control the oscillation frequency of the highfrequency power source (51) based on measurement results sequentiallyobtained due to selections made by the selector (43).

The output control circuit (44) may control the output electricity ofthe high frequency power source (51) to keep an electricity to besupplied to the impedance matching device constant, and the frequencycontrol circuit (45) may control the oscillation frequency of the highfrequency power source (51) to match the input impedance of theimpedance matching device (34) and the output impedance of the highfrequency power source (51).

The impedance matching device (34) comprises, for example, variablereactance elements (C1, C2), for matching the input impedance of theplasma generation electrode (5) and the output impedance of the highfrequency power source (51), and an impedance control circuit (46) whichcontrols element constants of the variable reactance elements (C1, C2)within a range which is preset for each process and which is restrictednarrower than an entire variable range of the variable reactanceelements.

To achieve the above objects, a plasma processing apparatus according toa second aspect of the present invention comprises:

-   -   a vacuum container (2) in which a process target is processed        with use of a plasma gas;    -   a plasma generation electrode (5) which is provided in the        vacuum container (2);    -   a high frequency power source (51) which generates a high        frequency electricity to be supplied to the plasma generation        electrode;    -   an impedance matching device (34) which includes variable        reactance elements (C1, C2) in order to match an input impedance        of the plasma generation electrode (5) and an output impedance        of the high frequency power source (51); and    -   an impedance control circuit (46) which controls element        constants of the variable reactance elements (C1, C2) included        in the impedance matching device (34) within a range which is        preset for each process for processing the process target and        which is restricted narrower than an entire variable range of        the element constants of the variable reactance elements (C1,        C2).

The impedance control circuit (46) controls the element constants of thevariable reactance elements (C1, C2) at, for example, an initial settingstage of each of a plurality of processes for processing the processtarget.

The impedance control means stores, for example, control data forcontrolling the element constants of the variable reactance elementsincluded in the impedance matching device within a range which isrestricted narrower than an entire variable range.

There may further be provided a phase difference sensor (41) whichmeasures a phase difference between a voltage component and a currentcomponent of an electricity supplied to the impedance matching device(34) from the high frequency power source (51), and an impedance sensor(42) which measures an input impedance of the impedance matching device(34), and the impedance control circuit (46) may control a capacitanceof a first variable capacitor (C1) included in the impedance matchingdevice (34) based on a measurement result from the phase differencesensor (41), and may control a capacitance of a second variablecapacitor (C2) included in the impedance matching device (34) based on ameasurement result from the impedance sensor (42).

To achieve the above objects, a plasma processing method according to athird aspect of the present invention is a control method of a plasmaprocessing apparatus which comprises a vacuum container in which asubstrate is processed with use of a plasma gas, a plasma generationelectrode which is provided in the vacuum container, a high frequencypower source which generates a high frequency electricity to be suppliedto the plasma generation electrode, and an impedance matching devicewhich matches an input impedance to the plasma generation electrode andan output impedance of the high frequency power source, the methodcomprising:

-   -   measuring by a power sensor, an electricity to be supplied to        the impedance matching device based on a difference between an        electricity of a progressive wave from the high frequency power        source and an electricity of a reflected wave to the high        frequency power source;    -   controlling by output control means, an output electricity of        the high frequency power source based on a measurement result        from the power sensor;    -   measuring by a phase difference sensor, a phase difference        between a voltage component and a current component of an        electricity to be supplied to the impedance matching device;    -   measuring by an impedance sensor, a level of an input impedance        to the impedance matching device; and    -   controlling by frequency control means, an oscillation frequency        of the high frequency power source based on measurement results        of the phase difference sensor and the impedance sensor.

The output control means may control the output electricity of the highfrequency power source to keep an electricity to be supplied to theimpedance matching device constant, and the frequency control means maycontrol the oscillation frequency of the high frequency power source tomatch the input impedance to the impedance matching device and theoutput impedance of the high frequency power source.

To achieve the above objects, a plasma processing method according to afourth aspect of the present invention is a control method of a plasmaprocessing apparatus which comprises a vacuum container in which asubstrate is processed with use of a plasma gas, a plasma generationelectrode which is provided in the vacuum container, a high frequencypower source which generates a high frequency electricity to be suppliedto the plasma generation electrode, and an impedance matching devicewhich matches an input impedance to the plasma generation electrode andan output impedance of the high frequency power source, the methodcomprising:

-   -   controlling element constants of variable reactance elements        included in the impedance matching device within a range which        is preset for each process for processing the substrate and        which is restricted narrower than an entire variable range of        the variable reactance elements.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing one example of a structure of a plasmaprocessing apparatus according to the embodiment of the presentinvention;

FIG. 2 is a diagram showing one example of a structure of a susceptor,etc. provided at the lower portion of a vacuum container;

FIG. 3 is a diagram showing one example of a structure of the upperportion of a vacuum container;

FIG. 4 is a diagram showing a structure of a connection part between animpedance matching device and a second high frequency power source;

FIG. 5 is a diagram showing an example of a structure representing astructure of a second high frequency power source;

FIG. 6 is a diagram showing one example of a structure of an impedancematching device;

FIG. 7 is a diagram showing an example of a structure representing astructure of an impedance control circuit shown in FIG. 6;

FIG. 8 is a diagram showing an example of data stored in a processcondition memory; and

FIG. 9A is a diagram showing changes in the capacitance of a variablecapacitor in a case where the variable range is narrowly restricted, andFIG. 9B is a diagram showing changes in the capacitance of a variablecapacitor in a case where the variable range is not restricted.

BEST MODE FOR CARRYING OUT THE INVENTION

A plasma processing apparatus according to the embodiment of the presentinvention will be explained below with reference to the drawings.

FIG. 1 is a diagram showing one example of a structure of a plasmaprocessing apparatus 1 according to the embodiment of the presentinvention.

This plasma processing apparatus 1 is constituted as a so-calledparallel plate type plasma processing apparatus having electrodesopposed to each other in parallel one above the other, and has afunction for forming a film such as an SiO₂ film, etc. on the surface ofa semiconductor substrate (hereinafter referred to as a wafer W).

With reference to FIG. 1, the plasma processing apparatus 1 comprises acylindrical vacuum container 2. The vacuum container 2 is made of aconductive material such as aluminum, etc. to which an almite process(anodic oxidation process) is applied. The vacuum container 2 isgrounded.

An exhaust pipe 3 is connected to the bottom of the vacuum container 2,and the exhaust pipe 3 is connected to a pump 4. The pump 4 is anexhaust device constituted by a turbo molecular pump (TMP) and the like,and can exhaust the vacuum container 2 of the air until the inside ofthe vacuum container 2 reaches a predetermined pressure.

A susceptor 8 for placing a wafer W thereon is provided at the lowercenter of the vacuum container 2. FIG. 2 is a diagram showing oneexample of a structure of the susceptor 8, etc. The susceptor 8 is madeof, for example, aluminum nitride (AlN) formed as a cylindrical shape.An electrostatic chuck 10 is placed and fixed on the upper surface ofthe susceptor 8, and the susceptor 8 functions as a lower electrode forgenerating plasma in the process space inside the vacuum pump 2.

The electrostatic chuck 10 is structured by disposing a conductive sheet10 a made of, for example, a copper foil plate, etc. between two upperand lower insulation layers made of, for example, polyimide films, andattracts a wafer W by Coulomb force to fix the wafer W thereon.

A heater 11 for heating the wafer W to a predetermined temperature isprovided in the susceptor 8. A refrigerant jacket 12 for circulating arefrigerant is provided so as to sandwich a thermoconductive plate 15between itself and the heater 11. An introduction pipe 13 and adischarge pipe 14 are connected to the refrigerant jacket 12, and arefrigerant supplied from the introduction pipe 13 circulates throughthe refrigerant jacket 12 and is discharged from the discharge pipe 14.The bottom surface of the susceptor 8 is supported by a ground member 2a which is a part of the inner wall of the vacuum container 2.

For example, inner conductive sticks 16, 17 a, and 17 b, and an outerconductive pipe 18 are connected to the susceptor 8. Through thesesticks and pipe, the susceptor 8 receives high frequency electricitygenerated by a first high frequency power source 50, and functions as alower electrode for introducing plasma toward the wafer W inside thevacuum container 2. Further, the inner conductive sticks 16, 17 a, and17 b, and the outer conductive pipe 18 function as an electricity supplystick 19 for supplying electricity to the lower electrode.

The inner conductive stick 16 is connected to the conductive sheet 10 acomprised by the electrostatic chuck 10, and conducts a high frequencyelectricity generated by the first high frequency power source 50 and adirect current voltage generated by a direct current power source 52.The inner conductive sticks 17 a and 17 b are connected to the heater11, and conduct electricity supplied from a commercial power source 53and having a commercial frequency. The outer conductive pipe 18 is apipe arranged so as to cover the inner conductive sticks 16, 17 a, and17 b.

As shown in FIG. 1, a matching box 20 having a matching circuit unit 21is provided between the susceptor 8, and the first high frequency powersource 50, direct current power source 52, and commercial power source53. The electricity supply stick 19 is drawn out from the external wallon the side surface of the vacuum container 2, such that it can beattached to the matching box 20.

The matching circuit unit 21 is provided for obtaining a match betweenthe output impedance of the first high frequency power source 50 and theinput impedance of the susceptor 8 functioning as the lower electrode.Further, the matching circuit unit 21 superimposes a voltage for plasmaintroduction supplied from the first high frequency power source 50 on adirect current voltage supplied from the direct current power source 52via a filter circuit constituted by an LPF (Low Pass Filter) or thelike, and outputs the superimposed voltage.

The matching box 20 couples the commercial power source 53 to the innerconductive sticks 17 a and 17 b, to enable supply of electricity havinga commercial frequency to the heater 11. A filter circuit constituted byan LPF or the like for preventing a high frequency electricity frombeing diverted into the commercial power source 53 may be providedbetween the matching box 20 and the commercial power source 53.

A shower head 5 having multiple gas ejection holes is provided to theceiling of the vacuum container 2 that is opposed to a placement surfaceof the susceptor 8 for placing the wafer W. The circumference of theshower head 5 is fixed to the vacuum container 2 by bolts and the like,and is covered with an insulation member 6 formed annularly. Theinsulation member 6 is made of quartz whose surface is covered with aninsulation film made of, for example, alumina (Al₂O₃) ceramics having ahigh corrosion-resistant property.

FIG. 3 is a diagram showing one example of a structure of the upperportion of the vacuum container 2 in detail. For example, two diffusionplates 7 a and 7 b are arranged at the upper portion of the shower head5. A plasma generation gas, a material gas, etc. are supplied to thediffusion plates 7 a and 7 b from gas pipes 26 a and 26 b which areconnected to the top of the diffusion plates 7 a and 7 b. A gas pipe 26including the gas pipes 26 a and 26 b is connected to a gas supplysource 29 via a valve 27 and an MFC (Mass Flow Controller) 28 as shownin FIG. 1, so that material gases such as SiH₄, and O₂, and a plasmageneration gas such as an Ar gas can be supplied from the shower head 5into the vacuum container 2. The gas pipe 26, the valve 27, the MFC 28,and the gas supply source 29 are provided in an appropriate pluralnumber in accordance with the kinds of gases to be provided into thevacuum container 2. However, FIG. 1 shows one of each of these. Thenumber and structure of the diffusion plates 7 a and 7 b may be changedappropriately in accordance with the kinds of gases to be supplied fromthe gas supply source 29.

An electricity supply stick 32 is coupled and fixed by screws, etc. ontothe upper surface of the diffusion plate 7 b at the center. By supplyinga high frequency electricity generated by a second high frequency powersource 51 to the shower head 5, the electricity supply stick 32 makesthe shower head 5 function as an upper electrode for generating plasmaof a material gas, etc. in the vacuum container 2.

An impedance matching device 34 is arranged above the vacuum container 2via a shield box 33. The impedance matching device 34 is provided forobtaining a match between the output impedance of the second highfrequency power source 51 and the input impedance of the shower head 5functioning as the upper electrode.

FIG. 4 is a diagram showing a structure of a connecting part between theimpedance matching device 34 and the second high frequency power source51. As illustrated, a power sensor 40, a phase difference sensor 41, animpedance sensor 42, a selection circuit 43, an amplitude controlcircuit 44, and a frequency control circuit 45 are provided to theconnection part between the impedance matching device 34 and the secondhigh frequency power source 51.

The power sensor 40 measures the electricity of a progressive wave fromthe second high frequency power source 51 and the electricity of areflected wave to the second high frequency power source 51 at an inputterminal of the impedance matching device 34 and calculates a differencebetween the measured electricity values, thereby measuring theelectricity of a high frequency to be supplied from the second highfrequency power source 51 to the impedance matching device 34.

The phase difference sensor 41 is provided for measuring a phasedifference between a voltage component and a current component of a highfrequency electricity to be input to the impedance matching device 34.

The impedance sensor 42 is provided for measuring the level of the inputimpedance of the impedance matching device 34. The impedance sensor 42obtains a current flowing to the input terminal of the impedancematching device 34 and a voltage of the input terminal, and derives theinput impedance from current/voltage.

The selection circuit 43 is provided for switching selection between thephase difference sensor 41 and the impedance sensor 42, and transmittingresults of detecting both of them to the frequency control circuit 45.

The amplitude control circuit 44 is provided for controlling the levelof a high frequency electricity output by the second high frequencypower source 51, based on a supply electricity (effective electricity)supplied to the impedance matching device 34 and measured by the powersensor 40. That is, the amplitude control circuit 44 makes it possiblefor stable plasma to be generated in the process space inside the vacuumcontainer 2 by adjusting an output electricity of the second highfrequency power source 51 such that the supply electricity (effectiveelectricity) measured by the power sensor 40 becomes a preset settingvalue. For example, the amplitude control circuit 44 adjusts the levelof a high frequency electricity to be output from the second highfrequency power source 51, by controlling a gain of a variable-gainamplifier included in the second high frequency power source 51.

The manner for the amplitude control circuit circuit 44 to control theamplitude of an output signal from the second high frequency powersource 51 is arbitrary. Therefore, the known proportion (P) control,integration (I) control, differentiation (D) control, and controls basedon the combination of those (PI control, PID control), etc. can be used.

For example, if it is assumed that a change amount of the amplitude ofan output signal from the second high frequency power source 51 is ΔA, adifference between an electricity measured by the power sensor 40 andthe set value is ΔP, and a, b, and c are coefficients, the control canbe performed in accordance with the equations below.ΔA=a·ΔP,ΔA=a·ΔP+∫b·ΔP,ΔA=a·ΔP+∫b·ΔP+c·dΔP/dt

The frequency control circuit 45 is provided for controlling anoscillation frequency of the second high frequency power source 51 basedon a phase difference between a voltage component and a currentcomponent measured by the phase difference sensor 41 and the inputimpedance of the impedance matching device 34 measured by the impedancesensor 42. For example, the second high frequency power source 51adjusts the oscillation frequency within a range of ±10% of apredetermined reference frequency, so that the phase difference betweena voltage component and current component of a high frequencyelectricity to be input to the impedance matching device 34 becomes 0,or that the level of the input impedance of the impedance matchingdevice 34 becomes 50ω.

The manner for the frequency control circuit 45 to control the frequencyof the second high frequency power source 51 is arbitrary. Therefore,the known proportion control, integration control, differentiationcontrol, and controls based on the combination of those can be used.

For example, if it is assumed that a change amount of the oscillationfrequency of the second high frequency power source 51 is Δf, the phasedifference between the voltage component and the current componentmeasured by the phase difference sensor 41 is, and a, b, and c arecoefficients, the control can be performed in accordance with thefollowing equation.Δf=a·+∫b·+c·d/dt

Further, for example, if it is assumed that a change amount of theoscillation frequency of the second high frequency power source 51 isΔf, a difference between the input impedance of the impedance matchingdevice 34 and 50ω is Δω, and d, e, and f are coefficients, the controlcan be performed in accordance with the following equation.Δf=d·Δω+∫e·Δω+f·dΔω/dt

FIG. 5 shows an example of a circuit structure of the second highfrequency power source 51. As illustrated, the second high frequencypower source 51 comprises a voltage control oscillator (VCO) 511 and ahigh frequency amplifier 512.

The voltage control oscillator 511 includes, for example, a PLL circuitand the like, and oscillates at a frequency subject to a control signalsupplied to an oscillation frequency control terminal Tfc from thefrequency control circuit 45.

The high frequency amplifier 512 has a structure of a variable gaintype, and amplifies an oscillation signal output from the voltagecontrol oscillator 511 by a gain subject to a control signal supplied toa gain control terminal Tac from the amplitude control circuit 44 andoutputs the amplified oscillation signal.

The impedance matching device 34 comprises variable capacitors C1 andC2, and an inductor L1 as shown in, for example, FIG. 6. Thecapacitances of the variable capacitors C1 and C2 are controlled by animpedance control circuit 46 at, for example, an initial setting time ineach process for processing the wafer W placed on the susceptor 8, inorder to match the output impedance of the second high frequency powersource 51 and the input impedance to the shower head 5.

The impedance control circuit 46 comprises a CPU (Central ProcessingUnit) or the like including, for example, a ROM (Read Only Memory) and aRAM (Random Access Memory), and is provided for controlling theimpedance of the impedance matching device 34. That is, the impedancecontrol circuit 46 adjusts the impedance of the impedance matchingdevice 34 when a process condition in the process space inside thevacuum container 2 is changed, to perform initial setting of theimpedance corresponding to each process condition. For example, theimpedance control circuit 46 matches the output impedance of the secondhigh frequency power source 51 and the input impedance to the showerhead 5 at around an initial value for the impedance which ispredetermined in accordance with a process condition, byrotation-driving a motor for rotating (or translating) electrodes of thevariable capacitors C1 and C2 included in the impedance matching device34.

To be more specific, the impedance control circuit 46 adjusts thecapacitance of the variable capacitor C1 at an initial setting stage ofeach process, based on a phase difference between a voltage componentand current component which are measured by the phase difference sensor41. For example, the impedance control circuit 46 adjusts thecapacitance of the variable capacitor C1, so that the phase differencebetween the voltage component and current component of a high frequencyelectricity to be input to the impedance matching device 34 at theinitial setting stage of each process will be 0.

Further, the impedance control circuit 46 adjusts the capacitance of thevariable capacitor C2 at the initial setting stage of each process,based on the level of the input impedance to the impedance matchingdevice 34 which is measured by the impedance sensor 42. For example, theimpedance control circuit 46 adjusts the capacitance of the variablecapacitor C2, so that the level of the input impedance to the impedancematching device 34 will be 5Ω at the initial setting stage of eachprocess.

The impedance control circuit 46 has a switching function, and canswitch so that it adjusts the capacitance of the variable capacitor C2based on a measurement result of the phase difference sensor 41 andadjusts the capacitance of the variable capacitor C1 based on ameasurement result of the impedance sensor 42.

The impedance control circuit 46 stores control data for adjusting theimpedance of the impedance matching device 34 to correspond to a matchpoint which is predicted before a wafer W is processed, for each of aplurality of process conditions for processing the wafer W in the vacuumcontainer 2, and adjusts the capacitances of the variable capacitors C1and C2 based on the control data. The control data is data for matchingthe impedances by limiting the variable range of the variable capacitorsC1 and C2 to a certain range which includes a match point predicted foreach process condition and which is restricted narrower than the entirevariable range of the variable capacitors C1 and C2.

The manner for the impedance control circuit 46 to control thecapacitances of the variable capacitors C1 and C2 is arbitrary, and theP control, the PI control, and the PID control, etc. which are describedabove can be used.

FIG. 7 shows an example of a circuit structure of the impedance controlcircuit 46. As illustrated, the impedance control circuit 46 comprises aCPU 61, A/D (analog/digital) converters 62 and 63, a process conditionmemory 64, and a driver circuit 65.

The A/D converter 62 A/D-converts a signal from the phase differencesensor 41 representing a phase difference between a current and avoltage, and supplies the signal to the CPU 61.

The A/D converter 63 A/D-converts a signal representing a phasedifference between a current indicative of an impedance from theimpedance sensor 42 and a voltage, and supplies the signal to the CPU61.

The process condition memory 64 is constituted by a non-volatile memory,and stores control data representing preset initial values of thecapacitances of the capacitors C1 and C2 and variable ranges, for aplurality of process conditions, as shown in FIG. 8. The control data isgenerated beforehand by calculation or based on experimental results. Asthe control data, for example, capacitances of the variable capacitorsC1 and C2 at which it is predicted that a match point for each processcondition exists, i.e. initial values for matching the impedances at theinitial setting stage of each process are stored. Further, a changechange range for changing the capacitances of the variable capacitors C1and C2 while each process is performed is stored. This change range isset as a narrower range than a range (entire variable range) in whichthe capacitances of the variable capacitors C1 and C2 is variable.

The driver circuit 65 changes the capacitances of the capacitors C1 andC2 by moving the electrodes of the capacitors C1 and C2 in accordancewith an instruction from the CPU 61.

At the beginning of a process, the CPU 61 instructs the driver circuit65 in accordance with a process instruction signal supplied from aprocess control apparatus or a control panel, to adjust the capacitancesof the variable capacitors C1 and C2 so that the impedance of theimpedance matching device 34 matches a match point predicted before awafer W is processed. Further, after a process is started, the CPU 61matches the output impedance of the high frequency power source 52 andthe input impedance of the upper electrode by limiting the variablerange of the variable capacitors C1 and C2 to a certain range whichincludes a match point predicted for each process condition and which isrestricted narrower than the entire variable range of the variablecapacitors C1 and C2, in accordance with a signal from the phasedifference sensor 41 and a signal from the impedance sensor 42.

An operation of the plasma processing apparatus 1 according to theembodiment of the present invention will be explained below.

When a wafer W is to be processed by the plasma processing apparatus 1,the wafer W is transported from, for example, an unillustrated load lockroom and placed on the susceptor 8. At this time, the wafer W isattractively fixed, by applying a direct current voltage generated bythe direct current power source 52 to the conductive sheet 10 a of theelectrostatic chuck 10. Then, the pump 4 is driven to vacuum the insideof the vacuum container 2 to a predetermined vacuum level. When thepredetermined vacuum level is reached, the valve 27 is opened. And apredetermined gas supplied from the gas supply source 29, for example, aplasma generation gas such as an Ar gas is introduced with its flow ratecontrolled by the MFC 28 into the gas pipe 26, then supplied into thevacuum container 2 by the shower head 5, and kept at a predeterminedpressure.

Further, the inside of the vacuum container 2 is heated by the heater11, and a predetermined material gas such as an SiH₄ gas and an O₂ gasis supplied from the gas supply source 29. The heater 11 heats theinside of the vacuum container 2 so that the temperature of the wafer Wwill be a predetermined process temperature within 400° C. to 600° C.

The first and second high frequency power sources 50 and 51 areactivated to begin supply of high frequency electricity, so that thematerial gas, etc. are plasma-decomposed and a laminated film isdeposited on the wafer W. At this time, the first high frequency powersource 50 applies a negative bias voltage to the conductive sheet 10 ain order to attract ions to the wafer W. The frequency of the first highfrequency power source 50 is determined based on a vibration frequencyand the like of the plasma ion inside the vacuum container 2, and is setto the maximum of approximately 10 MHz, and preferably to approximately2 MHz. The second high frequency power source 51 generates and outputs ahigh frequency electricity having a predetermined frequency within, forexample, 27 MHz to 100 MHz, preferably a frequency of 60 MHz.

The CPU 61 of the impedance control circuit 46 reads out the controldata stored in the process condition memory 64 at the initial settingstage of each process and adjusts the impedance of the impedancematching device 34. As described above, the control data is generatedbeforehand by calculation or based on experimental results, and storedin the process condition memory 64. According to this control data, thecapacitances of the variable capacitors C1 and C2 at which it ispredicted that a match point for each process condition exists, are setas the initial values for matching the impedances at the initial settingstage of each process.

The impedance control circuit 46 varies the capacitances of the variablecapacitors C1 and C2 in accordance with the control data, within apredetermined range which is restricted narrower than the entirevariable range of the variable capacitors C1 and C2, to adjust theimpedance of the impedance matching device 34. For example, let it beassumed that the process for the wafer W to be performed in the vacuumcontainer 2 includes a first and a second processes P1 and P2, theinitial value of the capacitance of the variable capacitor C1 that ispreset for the first process P1 is C11, and the initial value of thecapacitance of the variable capacitance C1 that is preset for the secondprocess P2 is C12. Here, the initial values C11 and C12 are respectivelyvalues corresponding to match points which are reproductive in the firstand second processes P1 and P2. The initial values C11 and C12 arestored in the process condition memory 64 shown in FIG. 8.

In this case, the impedance control circuit 46 adjusts the capacitanceof the variable capacitor C1 at around the initial value C11 at theinitial setting stage of the first process P1, so that the impedance ofthe plasma load and the output impedance of the second high frequencypower source 51 will match. That is, the impedance control circuit 46adjusts the capacitance of the variable capacitor C1 within a variablerange R1 which is preset for the first process P1 as shown in FIG. 9A,in order to match the impedances at around the initial value C11. Notethat a variable range R11 is limited narrower than the entire variablerange R1 of the capacitance of the variable capacitor C1.

Here, the output impedance of the second high frequency power source 51is normally 50ω. The characteristic impedance of a coaxial cable used asa wiring for connecting the second high frequency power source 51 andthe impedance matching device 34 is also normally 50ω. Accordingly, theimpedance control circuit 46 can obtain a match of the impedances byadjusting the capacitances of the variable capacitors C1 and C2 so thatthe level of the input impedance to the impedance matching device 34will be 50ω and a phase difference between a voltage component and acurrent component of a high frequency electricity input to the impedancematching device 34 will be 0.

Next, when the second process P2 is to start after the first process P1is finished, the capacitance of the variable capacitor C1 is adjusted toaround the initial value C12 preset for the second process P2 so thatthe impedances are matched. That is, the impedance matching circuit 46adjusts the capacitance of the variable capacitor C1 within a variablerange R12 preset for the second process P2 as shown in FIG. 9A, in orderto match the impedances at around the initial value C12. This variablerange R12 is also restricted narrower than the entire variable range R1of the capacitance of the variable capacitor C1.

FIG. 9B is a diagram showing changes in the capacitance of the variablecapacitor C1, in a case where the impedance of the impedance matchingdevice 34 is adjusted without such restrictions as described on thevariable ranges. As obvious from FIGS. 9A and 9B, by adjusting thecapacitance of the variable capacitor C1 within the variable ranges R11and R12 which are preset for the first and second processes P1 and P2,it is possible to shorten the time (matching time) required for theshift from the first process P1 to the second process P2. That is, T1<T2is achieved in FIGS. 9A and 9B.

Also for the capacitance of the variable capacitor C2, the impedancecontrol circuit 46 presets predetermined ranges that correspond to therespective process conditions and are restricted narrower than theentire variable range of the capacitance of the variable capacitor C2.Based on the preset ranges, the impedance control circuit 46 performsadjustment for matching the impedances at an initial setting stage ofeach process.

Because the impedances are matched by restricting the variable ranges ofthe variable capacitors C1 and C2 when a process condition changes withanother, it is possible to shorten the time required for matching theimpedances at the initial setting stage of each process. Further, it ispossible to avoid an accidental match at an unstable match point, and tothereby generate stable plasma in the vacuum container 2.

There is a case where the impedance of the plasma load changes after amatch of the impedances is obtained at the initial setting stage of eachprocess, due to fluctuation of the plasma density in the vacuumcontainer 2, etc. In this case, the frequency control circuit 45 reducesa reflected wave from the plasma load by restricting the oscillationfrequency of the second high frequency power source 51 based onmeasurement results of the phase difference sensor 41 and the impedancesensor 42.

The impedances of the reactance elements constituting the impedancematching device 34 such as the variable capacitors C1 and C2 and theinductor L1 change in accordance with frequency. Accordingly, if theoscillation frequency of the second high frequency power source 51 ischanged, the impedance of the impedance matching device 34 is alsochanged. Based on this, the impedance of the plasma load and theimpedance of the second high frequency power source 51 can be matchedand a reflected wave from the plasma load to the second high frequencypower source 51 can be reduced. Further, because the oscillationfrequency of the second high frequency power source 51 can beelectronically controlled, the impedance of the impedance matchingdevice 34 can be adjusted rapidly and precisely in accordance with achange in the impedance of the plasma load.

At this time, the amplitude control circuit 44 can make plasma to begenerated in the vacuum container 2 stable so that the wafer W can beprocessed appropriately, by adjusting the output electricity of thesecond high frequency power source 51 in a manner that the supplyelectricity (effective electricity) measured by the power sensor 40 iskept at a fixed amount.

In a case where, for example, an SiH₄ gas and an O₂ gas are supplied asmaterial gases, these gases are ionized in the process space in thevacuum container 2, and thus an SiO₂ film is deposited on the wafer W.When the deposition of the laminated film is finished, supply of thedischarge electricity, introduction of the material gases, and heatingof the inside of the vacuum container 2 are stopped, and the inside ofthe vacuum container 2 is sufficiently purged and cooled. Thereafter,the wafer W is taken out.

As explained above, according to the present embodiment, the impedanceof the impedance matching device 34 is controlled to obtain a match, byadjusting the capacitances of the variable capacitors within rangespreset for each process at the initial setting stage of the process forprocessing the wafer W. Therefore, it is possible to obtain a match ofthe impedances in a short time at the initial setting stage of eachprocess and to shorten the time required for processing of a substrate.

Further, according to the present embodiment, it is possible to keep theelectricity to be supplied to the plasma load constant, by matching theimpedances by controlling the oscillation frequency and outputelectricity of the second high frequency power source 51 by theamplitude control circuit 44 and the frequency control circuit 45. Dueto this, it is possible to adjust the impedance rapidly and precisely inaccordance with a change in the impedance of the plasma load, andthereby to process the wafer W by generating stable plasma.

The present invention is not limited to the above-described embodiment,but can be variously modified and applied. For example, theabove-described embodiment explains that after a match is obtained bythe impedance control circuit 46 adjusting the impedance of theimpedance matching device 34 at the initial setting stage of eachprocess, the oscillation frequency and output electricity of the secondhigh frequency power source 51 are controlled by the amplitude controlcircuit 44 and the frequency control circuit 45. However, the presentinvention is not limited to this, but a match of the impedances may beobtained by controlling the oscillation frequency and output electricityof the second high frequency power source 51 by the amplitude controlcircuit 44 and the frequency control circuit 45 also at the initialsetting stage of each process.

Further, according to the above-descried embodiment, the control formatching the impedances is performed in the circuit for supplying a highfrequency electricity to the shower head 5 which functions as the lowerelectrode. However, the present invention is not limited to this, but asimilar control may be performed in a circuit for supplying a highfrequency electricity to the susceptor 8 which functions as the lowerelectrode.

Further, the variable capacitors C1 and C2 of the impedance matchingdevice 34 need not to be constituted limitedly by those which haveelectrodes whose positions are changed, but may be constituted byvariable capacitance diodes or the like. Further, the impedance matchingdevice 34 needs not to comprise those which have variable capacitances,but may comprise variable inductors. In this case, a similar control tothat of the case of comprising variable capacitors can be performed bystoring in the impedance control circuit 46, control data which issuited to the variable inductors. That is, the impedance matching device34 needs only to comprise variable reactance elements, whose elementconstants can be adjusted by the impedance control circuit 46.

Further, the plasma processing apparatus 1 of the present inventionneeds not to comprise all of the components described above, but maycomprise a part of those. For example, the plasma processing apparatus 1may be so structured as to comprise the amplitude control circuit 44 andthe frequency control circuit 45, but not the impedance control circuit46. Further, the plasma processing apparatus 1 may be so structured asnot to comprise the amplitude control circuit 44 and the frequencycontrol circuit 45, but comprise the impedance control circuit 46.

The structure of the plasma processing apparatus 1 may be arbitrarilychanged. For example, the plasma processing apparatus 1 may comprise acoil or a permanent magnet for causing a predetermined magnetic fieldaround the vacuum container 2, in order to process the wafer W byutilizing electron cyclotron resonance.

Further, the present invention is not limited to a plasma processingapparatus for performing a plasma CVD process, but may be applied to anetching apparatus, a ashing apparatus, etc. as long as they are anapparatus for supplying a high frequency electricity to a shower headand a susceptor and plasma-processing a process target such as asemiconductor wafer, an LCD substrate, and a solar battery substrate.

This application is based on Japanese Patent Application No. 2001-380196filed on Dec. 13, 2001 and including specification, claims, drawings andsummary. The disclosure of the above Japanese Patent Application isincorporated herein by reference in its entirety.

Industrial Applicability

The present invention can be applied to a plasma processing apparatussuch as a semiconductor manufacturing apparatus, and a liquid crystaldisplay element manufacturing apparatus, and to a plasma processingmethod.

1. A plasma processing apparatus comprising: a vacuum container (2) inwhich a substrate is processed with use of a plasma gas; a plasmageneration electrode (5) which is provided in said vacuum container; ahigh frequency power source (51) which generates a high frequencyelectricity to be supplied to said plasma generation electrode (5); animpedance matching device (34) which matches an input impedance of saidplasma generation electrode (5) and an output impedance of said highfrequency power source (51); an impedance sensor (42) which measures alevel of an input impedance of said impedance matching device; and afrequency control circuit (45) which controls an oscillation frequencyof said high frequency power source based on a measurement result fromsaid impedance sensor.
 2. The plasma processing apparatus according toclaim 1, further comprising a phase difference sensor (41) whichmeasures a phase difference between a voltage component and a currentcomponent of an electricity to be supplied to said impedance matchingdevice, wherein said frequency control circuit (45) controls theoscillation frequency of said high frequency power source based onmeasurement results from said phase difference sensor and said impedancesensor.
 3. The plasma processing apparatus according to claim 1, furthercomprising: a power sensor (40) which measures an electricity to besupplied to said impedance matching device from said high frequencypower source; and an output control circuit (44) which controls anoutput electricity of said high frequency power source based on ameasurement result from said power sensor.
 4. The plasma processingapparatus according to claim 2, further comprising: a power sensor (40)which measures an electricity to be supplied to said impedance matchingdevice from said high frequency power source; and an output controlcircuit (44) which controls an output electricity of said high frequencypower source based on a measurement result from said power sensor. 5.The plasma processing apparatus according to claim 4, comprising aselector (43) which switches selection between said phase differencesensor (41) and said impedance sensor (42) to obtain measurement resultsfrom both of them, wherein said frequency control circuit (45) controlsthe oscillation frequency of said high frequency power source (51) basedon measurement results sequentially obtained due to selections made bysaid selector (43).
 6. The plasma processing apparatus according toclaim 4, wherein: said output control circuit (44) controls the outputelectricity of said high frequency power source (51) to keep anelectricity to be supplied to said impedance matching device constant;and said frequency control circuit (45) controls the oscillationfrequency of said high frequency power source (51) to match the inputimpedance of said impedance matching device (34) and the outputimpedance of said high frequency power source (51).
 7. The plasmaprocessing apparatus according to claim 4, wherein said impedancematching device (34) comprises: variable reactance elements (C1, C2),for matching the input impedance of said plasma generation electrode (5)and the output impedance of said high frequency power source (51); andan impedance control circuit (46) which controls element constants ofsaid variable reactance elements (C1, C2) within a range which is presetfor each process and which is restricted narrower than an entirevariable range of said variable reactance elements.
 8. A plasmaprocessing apparatus comprising: a vacuum container (2) in which aprocess target is processed with use of a plasma gas; a plasmageneration electrode (5) which is provided in said vacuum container (2);a high frequency power source (51) which generates a high frequencyelectricity to be supplied to said plasma generation electrode; animpedance matching device (34) which includes variable reactanceelements (C1, C2) in order to match an input impedance of said plasmageneration electrode (5) and an output impedance of said high frequencypower source (51); and an impedance control circuit (46) which controlselement constants of said variable reactance elements (C1, C2) includedin said impedance matching device (34) within a range which is presetfor each process for processing the process target and which isrestricted narrower than an entire variable range of the elementconstants of said variable reactance elements (C1, C2).
 9. The plasmaprocessing apparatus according to claim 8, wherein said impedancecontrol circuit (46) controls the element constants of said variablereactance elements (C1, C2) at an initial setting stage of each of aplurality of processes for processing the process target.
 10. The plasmaprocessing apparatus according to claim 8, wherein said impedancecontrol means stores control data for controlling the element constantsof said variable reactance elements included in said impedance matchingdevice within a range which is restricted narrower than an entirevariable range.
 11. The plasma processing apparatus according to claim8, comprising: a phase difference sensor (41) which measures a phasedifference between a voltage component and a current component of anelectricity supplied to the impedance matching device (34) from saidhigh frequency power source (51); and an impedance sensor (42) whichmeasures an input impedance of said impedance matching device (34),wherein said impedance control circuit (46) controls a capacitance of afirst variable capacitor (C1) included in said impedance matching device(34) based on a measurement result from said phase difference sensor(41), and controls a capacitance of a second variable capacitor (C2)included in said impedance matching device (34) based on a measurementresult from said impedance sensor (42).
 12. A control method of a plasmaprocessing apparatus which comprises a vacuum container in which asubstrate is processed with use of a plasma gas, a plasma generationelectrode which is provided in said vacuum container, a high frequencypower source which generates a high frequency electricity to be suppliedto said plasma generation electrode, and an impedance matching devicewhich matches an input impedance to said plasma generation electrode andan output impedance of said high frequency power source, said methodcomprising: measuring by a power sensor, an electricity to be suppliedto said impedance matching device based on a difference between anelectricity of a progressive wave from said high frequency power sourceand an electricity of a reflected wave to said high frequency powersource; controlling by output control means, an output electricity ofsaid high frequency power source based on a measurement result from saidpower sensor; measuring by a phase difference sensor, a phase differencebetween a voltage component and a current component of an electricity tobe supplied to said impedance matching device; measuring by an impedancesensor, a level of an input impedance to said impedance matching device;and controlling by frequency control means, an oscillation frequency ofsaid high frequency power source based on measurement results from saidphase difference sensor and said impedance sensor.
 13. The controlmethod according to claim 12, wherein: said output control meanscontrols the output electricity of said high frequency power source tokeep an electricity to be supplied to said impedance matching deviceconstant by controlling the output electricity of said high frequencypower source; and said frequency control means controls the oscillationfrequency of said high frequency power source to match the inputimpedance to said impedance matching device and the output impedance ofsaid high frequency power source.
 14. A control method of a plasmaprocessing apparatus which comprises a vacuum container in which asubstrate is processed with use of a plasma gas, a plasma generationelectrode which is provided in said vacuum container, a high frequencypower source which generates a high frequency electricity to be suppliedto said plasma generation electrode, and an impedance matching devicewhich matches an input impedance to said plasma generation electrode andan output impedance of said high frequency power source, said methodcomprising: controlling element constants of variable reactance elementsincluded in said impedance matching device within a range which ispreset for each process for processing the substrate and which isrestricted narrower than an entire variable range of said variablereactance elements.